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The importance of temporal synchrony in word recognition

University of British Columbia

The primary purpose of this study was to examine the effect of temporal asynchrony on recognition of words presented in background noise. This was done by determining if participants' ability to recognize and repeat words from monaural, highland low-context sentences worsened when: (1) the signal-to-noise ratio decreased (where the noise was multi-talker "babble" presented simultaneously with the signal); and (2) the degree of temporal asynchrony ("jitter") increased. The other purpose of this study was to determine if monaural temporal processing ability (as measured by performance on the "jitter" task) correlated with variables such as gap threshold, age, education, or vocabulary size. In this experiment, 16 young, normal-hearing participants (ages 18-35) repeated the last word of SPIN-R sentences altered by differing degrees of temporal jitter. In addition to one condition where the SPIN-R sentences were unchanged, three jitter conditions were tested: two were moderate degrees of jitter that differed in sound quality and method of creation, and one was a highly jittered condition. Jittered and unjittered stimuli were presented in signal-to-noise ratios of +4 and +8 dB, to examine the interaction effects of temporal asynchrony and background noise on word recognition. Participants also performed a gap detection task (Schneider, 1994), the 20-item Mill Hill Vocabulary test (Raven, 1938), and pure-tone air conduction and SRT tasks. It was found that degree of temporal jitter, signal-to-noise ratio and context all had significant effects on participants' abilities to recognize sentence-final words. One of the moderate jitter conditions affected participants' performance on low-context sentences. Specifically, with a moderate amount of jitter and without context, participants could not accurately repeat all sounds in the target word, and tended to replace one or more sounds with others containing similar phonetic features. The highly jittered condition adversely affected performance on both the high- and low-context sentences; that is, with this degree of jitter, context was no longer enough to help listeners anticipate the sentence-final words, and perceptual errors increased dramatically - particularly in the lower signal-to-noise ratio. Participants' performance on the jittered SPIN task resembled that of elderly listeners on unjittered sentences (Pichora-Fuller, Schneider, & Daneman, 1995). This suggests that the external jitter tested in this study may be similar to that hypothesized to characterize the aging auditory system, and which is thought to interfere with the ability of the elderly to understand language spoken in noisy environments. It was also found that performance on the SPIN task did not correlate with gap threshold, age, years of education, or vocabulary-test score. However, the participants in this study were of similar ages and years of education, and performed similarly on the gap and vocabulary tests. (In addition, a learning effect was found for the gap detection task.) Thus this sample was not representative of all possible participants, and conclusions about correlations must be made cautiously.

Thesis/Dissertation

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2009-05-26

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http://hdl.handle.net/2429/8199

Audiology and Speech Sciences

University of British Columbia

UBCV

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